Electric switch



Feb. 8, 1938. s. R. SMITH ELECTRIC SWITCH Filed Jan. 25, 1935 2 Sheets-Sheet l Feb. 8, 1938. s, R@ SWTH 2,107,651

ELECTRIC SWITCH Filed Jan. 25, 1935 2 Sheets-Sheet 2 67 242/ 66 Z5 27 26 4/ 9 5/ j 5 22 gl.. ..LL'L k 52 .a \50 \25 1:11 .::2 5l 6@ i5 37 TTORNEKS Patented Feb. 8, 1938 ELECTRIC SWITCH Sidney Reynell Smith, Liverpool, England, as-

signor, by mesne assignments, to Automatic Telephone & Electric Company Limited, London, England Application January 25, 1935, Serial No. 3,371 In Great Britain February 15, 1934 2 Claims.

The present invention relates to electric switches and is more particularly concerned with pressure-operated switches of the type inserted in the road surface to act as vehicle detectors in Vehicle-actuated traffic control systems. In wellknown prior constructions of this type, the weight or vehicles traversing the detector flexes a resilient conductor sheet into contact with another conductor sheet to complete an electrical circuit. In such prior arrangements the springiness of the resilient conductor sheet is primarily relied upon to separate the electrical contacts when the vehicle had passed off it.

In the construction according to the present invention, the resilient conductor sheet is retained but its resiliency plays little or no part in bringing about the separation of the contact sheets since it is now supported by other resilient means which may be subjected to great strain without the possibility of its taking on a permanent set.

According to another feature of the invention, the resilient conductor sheet may be readily removed for examination or replacement without disturbing the complete detector assembly or electrical wiring.

The invention will be better understood from the following description of one way of carrying it into effect, which will be explained in connection with the accompanying drawings.

Figure 1 shows a plan View of the vehicle detecting unit.

Figure 2 is a section view along the line 2-2 of Figure l.

Figure 3 is a section view' along the line 3-3 of Figure 1.

Figure 4 is a section View along the line 4-4 of Figures 2 and 5, and

Figure 5 is a section view along they line 5 5 of Fig. l. y

Referring to Figure 5, it will be appreciated that the unit comprises a substantial tread member El of moulded rubber which seats between two shoulders 22, welded on a metal bed plate 23 and is clamped into position by metal strips of L section 24 which run the full length of the detector and register with moulded grooves in the tread member. The purpose of these grooves is to prevent the tread being stroked out of position by the continuous impact of heavy vehicles. The resilient conductor sheet 25 is shown accommodated in slots in the tread member into which it may be inserted lengthways but it could also be moulded and if necessary provided with suitable projections or ears to ensure that it should maintain its position. The eiect in either case is that the sheet 25 is suspended over a pair of contact bars 21, 28 lying side by side on a hard rubber bed 29. Two contact members 21, 28 are provided to adapt the unit to detect traine passing in one direction only, and the manner in which this may be effected follows:

When a Vehicle passes over the unit the rubber tread is depressed and carries with it the resilient conductor sheet 25 which rst comes into engagement with the contact bar lying nearer the point of application of the pressure and as the traffic passes over the detector the resilient sheet then bridges both Contact bars. The movement produced is of a rolling type and when the vehicle leaves the detector the rubber tread 2l resumes its normal position and lifts the resilient sheet 25 clear of both contact bars 21, 28.

The `contact bars 21, 28 are securely fastened to the hard rubber bed plate 29 by a number of screws 3, in the manner shown in Figures 1, 4, and 5, and the mounting is suniciently robust to support the traffic passing over them. Alternatively, if unidirectional detection is not required, the two bars 21, 28 could be connected together so as to have the same eiect or be replaced by one bar of double width. Rubber studs 32 are provided at intervals along the tread member on both sides of the cavity carrying the resilient strip 25 and their function is to ensure that the strip shall not come into contact with the bars in case the tread should become distorted after long use.

The cables for extending the electrical connections to the contact bars and flexible plate terminate in a separate chamber 40. Referring now to Figures 1, 2, and 3, it will be noted that this chamber or splice box is located at the side of the detector, rather than at its end, so as to avoid introducing a dead spot, or region in the detector not sensitive to pressure actuations. The actual connections to the contact bars and ilexible steel plate element are effected by means of springy strips of metal, 4|, 42, 43, and as shown in Figure 2 the left hand contact bar 21 has riveted to its underside a U-shaped springy connecting link 42 which is accommodated in a slot 45 in the hard rubber bed plate 29 and is held in position by two bolts 46 which pass through the main bed plate 23 and are threaded into a brass bar 48 provided with a terminal 49 at its end. Insulating bushings 54, and pads 5U, 5| are provided to prevent contact with the metal bed plate 23 which is at earth potential. Connection with the right hand contact bar 28 is effected by another piece of springy material 43, which is accommodated in a further cavity 55 in the hard rubber bed plate 29 and is of angular shape as indicated in Figures 1 and 4, the free end rising to connect with the underside of the bar 28.

Connection with the resilient contact strip is effected in the manner shown more clearly in Figure 3. The sides of the cavity in the tread 2l supporting the strip: 25 are cut away for an inch or so, so that the strip projects for this distance unsupported and establishes rubbing contact with the U-shaped spring member 4l shown. A metal block 51 is provided underneath the free end of the spring 4l about the area where it contacts with the resilent conductor 25, to form a stop for limiting the movements of the spring and to prevent it from becoming distorted in the event of heavy traffic passing over this particular point in the detector. In this case also, external connection from the spiing is made through the fastening bolts 56 and, as shown in Figure l, the three terminal members 48, 58, 68, are supported by the bridge pieces 52, 53 at the point Where they enter the splicing chamber 4U to withstand the strain of the connecting cable. As will be appreciated from Figures 2 and 3, the splice box 40 is welded to the bed plate 23 of the detector unit and is provided with inlet conduit 3l and outlet conduit for accommodating the connecting cables to the control equipment.

The complete assembly described is arranged to be embedded in a concrete foundation in the road and will preferably be provided with bars or ns (not shown), around which the concrete sets to anchor the unit rmly to the road surface. It will be appreciated that if it is desired to gain access to the contacts 25, 21, 28, after the detector has been installed it is only necessary to remove the screws 3l holding the clamping members 24 and lift out the rubber tread member 2l. rI'his may subsequently be replaced or a new tread member may be substituted without disturbing the electrical connections.

Thus the several objects specically brought out above, and others, are achieved. It is to be understood that various modifications in the structural details or arrangement of the parts, or changes in the designs herein exemplified may be made Without departing from the spirit of the invention as dened by the claims.

Having described my invention what I claim as new and desire to secure by Letters Patent of the United States is:

1. In a vehicle operated switch, the combination of a relatively long and narrow receptacle adapted to be imbedded substantially horizontally in the roadway for operation by vehicles passing thereover, a stationary contact bar extending longitudinally in Said receptacle, a resilient insulating cover mounted in said receptacle, said cover having projecting portions extending downward and longitudinally thereunder and formed with slotted recesses extending longitudinally and horizontally in said projecting portions with the open edges of said recesses spaced laterally in opposed relation to each other, and a contact strip slideably mounted in said recesses so as to be resiliently supported by said cover for engagement with said stationary contact bar only under pressure by vehicles on said cover.

2. In a traffic operated circuit closer, a substantially rigid and relatively long and narrow receptacle, a contact bar mounted therein, a resilient insulating cover removably mounted in said receptacle and forming a cavity over said contact bar and providing slotted recesses extending horizontally and longitudinally along its inner walls with the open edges of the recesses spaced laterally opposite each other, and a flexible contact strip detachably mounted in said slotted recesses so as to be normally supported out of engagement with said bar and for engaging said bar upon pressure applied to the outer surface of said cover and upon release of presn sure being restored by resilience of the cover to normal position.

SIDNEY REYNELL SMITH. 

